This description relates to detecting and using body tissue electrical signals.
The peripheral nerves in a human body, for example, produce and propagate electrical signals (sometimes called impulses) to do various jobs. Efferent nerves, for example, propagate signals from the central nervous system to muscles of the extremities to cause contraction or relaxation of the muscles. (For simplicity, we sometimes use the term “contraction” to refer to both contraction or relaxation.) Afferent nerves propagate signals in the other direction, from sensory organs including the skin to the central nervous system. One way to detect nerve electrical signals (impulse activity) is by the invasive technique of inserting an electrode through the skin and into the nerve; the nerve electrical signals can then be detected at the exposed end of the electrode.
Contraction or relaxation of muscles is caused by neurons at locations in the vicinity of, for example, muscles that operate the fingers. To activate a particular muscle (e.g., to cause it to contract), the brain can send a signal to a particular selected nerve having a bundle of neurons to cause the neurons to produce electrical signals. These electrical signals are based on the chemical process of interaction between neurons and between neurons and effector cells through the chemical messengers or neurotransmitters that are released. In the case of skeletal muscle cells, activated motor neurons transmit the neurotransmitter acetylcholine to the synapses of the skeletal muscle cells allowing the ion channels in that cell to open. This changes the membrane potential of the cell resulting in the sequence of events that causes an action potential and then a contraction of the muscle.
By sending coordinated electrical signals through selected nerves to corresponding muscles associated with a particular finger, for example, the brain can cause the finger to produce a wide variety of actions such as touching the palm. Thus, the brain can send signals through nerves to muscles in various parts of the body to cause parts of the body to move according to gestures intended by the brain, such as raising the index and middle finger of a hand in a “V”. The gestures in turn can represent intent, for example, the intent to congratulate a teammate on a victory.
Other tissues of the body, such as brain cells, interneurons, and bones (which exhibit piezoelectric properties), also can produce electrical signals. Electrical signals produced by some tissues of the body are sometimes called action potentials.